It is known from U.S. Pat. No. 5,297,611 and its division, U.S. Pat. No. 5,477,906, to produce aluminum-alloy cylinder blocks wherein a thermal gradient is formed in the cast piece during cooling to promote controlled solidification of the liquid aluminum-alloy within a sand mold by the utilization of heat-conductive inserts (which function as heat sinks and in the industry are generally called “chills”). To function as a heat-sink, the chill plate has mass (usually of iron) that at least begins at a temperature lower than the solidification temperature of the aluminum alloy. It thus promotes early solidification of the block starting at the surface of the chill in contact with the newly cast block. The chill is typically placed so that the solidification is directed to proceed in a direction towards the source of molten metal, usually at the opposite end of the block. This avoids premature solidification in areas that would block access to the source of molten metal (which blockage prevents filling in detrimental voids that can otherwise be caused by the shrinkage resulting from cooling during solidification of the casting). The utilization of such chills aids in producing high-quality engine blocks, because the liquid aluminum solidifies in a more orderly manner thereby helping to eliminate such voids and associated shrinkage porosity which often occur when the block is allowed uncontrolled solidification in all directions.
Although there are suggestions in the prior art that the chill or thermal core can be brought into contact with an external heat sink or other heat extraction means so as to maintain a continuing heat extraction from the casting throughout the solidification step, said patents are vague with respect to a practical way of achieving such heat extraction. They refer to some means for continuously removing heat from the solidifying melt to thereby develop and maintain the strong thermal gradients necessary to achieve directional solidification, and teach two general ways of achieving this cooling: (a) by increasing the heat extraction area of the chill by providing it with cooling fins (which then may be contacted with forced cooling air or mist, as needed); and (b) by providing a channel through said chill for allowing water to be circulated to cool the chill.
These and other currently-used chills do provide means for promoting directional solidification. However, the applicants have discovered that more rapid and better-controlled directional solidification, with consequent improved quality of the castings, can be achieved by carefully controlled selective direct water impingement on specific areas of the solidifying casting. This is accomplished in part by utilizing sand molds and/or cores that are formed with a water-soluble binder which are at least partially removed by jets of water to cool and quickly begin to play directly on the selected newly-solidified metal skin of the casting, thus resulting in a greater thermal gradient in and a more rapid cooling of the casting, whereby the solidification of the block is thereby improved and strongly driven in the desired direction.
Part of this improvement is well described in the recently published U.S. pat. application No. 2004/0050524 A1 (filed Mar. 18, 2004 and entitled “Mold-Removal Casting Method and Apparatus”). This and all patents or other documents cited in this text, and all documents cited or referenced in the documents cited in this application as filed, are incorporated herein by reference. Documents incorporated by reference into this application or any teachings therein may be used in the practice of this invention.
However, there remain significant drawbacks to the teaching and disclosure in the 2004/0050524 publication. The water soluble binders typically are of higher cost and may have less desirable molding attributes. In addition, it can be difficult to control the specific application of the cooling water (or solvent) to precisely defined and delimited areas of the complex casting (needed to achieve the most effective control over the site of the cooling to give the best and directional accuracy of cooling and thereby of the controlled solidification progression therefrom to obtain the desired high quality results).